1. Field of the Invention
This invention relates generally to voltage detector design and, more particularly, to the design of a three-level voltage detector.
2. Description of the Related Art
Comparators are devices that typically compare two voltages or two currents, switching their respective outputs to indicate which of the two input signals is larger. Oftentimes comparators are analog circuits used in a variety of applications. One implementation and use of comparators may be directed towards detecting the level of an input signal, for example an input voltage, relative to a designated reference level or multiple reference levels. Certain applications may call for voltage detectors that accurately detect a high voltage state (Vdd), a low voltage state (Gnd), and/or an open state on an IC (integrated circuit) pin.
Current solutions generally detect the high and the low states but require external components to detect the open state. Furthermore, the range of the open condition is typically static, and the detectors normally remain turned on, drawing supply current even after the input state has already been determined. A typical example of a three-level voltage detector 100 is shown in FIG. 1. Comparators 106 and 108 are used to check the level of input signal 120 against a high voltage 110 and a low voltage 112, respectively. As shown, input signal 120 may be present as one of several possible external connections that include Vdd, Gnd, or an intermediate voltage obtained from a voltage divider circuit comprising resistors 102 and 104. As seen in FIG. 1, external resistors (102 and 104) are required when operating voltage detector 100.
Other corresponding issues related to the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.